Have you ever seen the moon? The modern character 月 does not look like the moon at all. Ponte Ryuurui writes:
Originally, 月 was written the way we see the crescent Moon from the Earth. In the process of stylisation it was turned on its axis. It is important to remember that at that time, for a period of some 2000 years (often referred to as The Age of Bamboo Slips), many characters were written on narrow bamboo (or other wood) planks <...> Due to their oblong nature, many characters were elongated when written.Many historical forms of the character indeed look more like a crescent moon.